In connection with the operation of large semitrailer trucks, the tractor unit is used to transport the trailer unit to a distant point. When the trailer unit has been delivered, the tractor unit does not become a useful work vehicle, unless there is another trailer available which is to be transported. With the development of the portable flatbed unit of the present invention, after a trailer has been delivered, it is possible to convert the tractor unit into a flatbed truck. Accordingly, when the semi-trailer truck has reached its destination and the trailer has been disembarked, it is possible to convert the vehicle to a flatbed truck either for local hauling or long distance hauling. In this manner, the likelihood of a tractor unit having to be transported a long distance without a load is substantially diminished.